The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In a plate fin type heat exchanger proposed in JA-A-2002-340490, plate fins are mechanically connected to a tube by expanding the tube. In order to enhance performance, a flat tube having a flat cross section is used, and a radius of curvature on an inner wall side at an end in a direction of long diameter of the cross section is at least ½ of a size in a direction of short diameter on the inner wall side nearly at the center in the direction of long diameter. With this, when the tube is expanded, the whole outer periphery of the tube can be nearly uniformly expanded to prevent the tube from being cracked or broken to enhance durability.
However, an end portion in a longitudinal direction of tube is bonded to a header plate (core plate) by use of brazing (soldering) or an adhesive made of thermosetting resin material. For this reason, a furnace at high temperature is required and energy consumption is increased in a manufacture. In view of the fact that the reduction of CO2 is strongly required in recent years so as to prevent global warming, the inventors think that the reduction of energy consumption is extremely important.